Conventionally, imaging devices such as television cameras are configured to use clamping to set the black level of the imaging result to a predetermined signal level. For example, CCD solid-state image sensors use sensor portions arranged in a matrix to photoelectrically convert incident light and sequentially transfer and output stored charges obtained as a result. CCD solid-state image sensors are configured in such a way that a partial region of an imaging surface comprising the sensor portions arranged in a matrix in this way is shielded from light to create an optical black region, and the optical black level can be detected by the output signal level of this optical black region. Because of this, imaging devices are configured to integrate the output signals of imaging elements obtained from the optical black region to obtain a predetermined evaluation value and offset the output signal levels of the imaging elements so that this evaluation value becomes a predetermined value, thereby forming a feedback loop to set the black level of the imaging result to a predetermined signal level.
However, in these imaging devices, when the signal level of the imaging result obtained from the optical black region momentarily changes due to noise getting mixed in, the evaluation value temporarily changes, and the black level needs to be corrected to correct this change.
Japanese Patent Application Laid-open (JP-A) No. 2003-110943 discloses a technology which, in an imaging device, detects an optical black level resulting from an output signal level of an optical black region in which a partial region of an imaging surface has been shielded from light and offsets the output signal level of an imaging element in accordance with the detection value. Specifically, the imaging device integrates, by frame, the luminance level obtained from the optical black region to detect an evaluation value representing the optical black level of the imaging result, uses this integrated value as a detection value resulting from detection data, offsets the luminance level of image data using a correction value based on this, and performs processing that clamps the black level of the imaging result to a predetermined signal level.
Furthermore, in recent years, digital imaging devices that use flat panel radiation detectors—or what are called flat panel detectors (FPDs)—having a phosphor and a large-area amorphous silicon sensor in close contact to directly digitalize a radiographic image without involving an optical system or the like have come into practical use. Furthermore, FPDs that use amorphous selenium, lead iodide (PbI2), and mercury iodide (HgI2), for example, to convert radiation into electrons and use a large-area amorphous silicon sensor to detect the electrons have similarly come into practical use. These FPDs show promise as next-generation digital imaging devices because in principle they are capable of capturing not only still images but also moving images.
The sensors used in FPDs comprise several million pixels, and the characteristics of the pixels differ from one another. The characteristics particularly important for image sensors are the dark current characteristic and the sensitivity characteristic. Therefore, in FPDs, offset correction for correcting these characteristics is implemented, and the sensors are used as sensors in which the characteristics of the pixels are substantially uniform.